Select the same tool, whose icon has slightly changed and whose tooltip now says Disconnect from Browser.

If you had originally opened the browser through one of the Engineering Links tools or by choosing Connect Web Browser, selecting Disconnect from Browser closes the browser in addition to disconnecting it from OpenPlant Modeler . If you had opened the browser from outside OpenPlant Modeler and then connected to it, selecting Disconnect from Browser only disconnects OpenPlant Modeler from the browser without closing the browser.